Electronic devices and multilayered wiring boards, etc. have been increasingly microsized and highly integrated, and an insulating film having a lower relative permittivity is required for application thereto. In order to satisfy such a requirement and to secure heat resistance of at least 350° C., preferably at least 425° C., which is required in the process for producing electronic devices or multilayered wiring boards, fluorinated aromatic polymers (hereinafter referred to as FAP) are being studied.
For example, Japanese Patent 3,064,011, U.S. Pat. Nos. 5,115,082, 5,959,157, JP-A-9-202824, JP-A-10-247646, J. Polm. Sci.; Part A; Polm. Chem., vol. 36, 2881 (1998), etc. disclose fluorinated aromatic polymers having ether linkages (hereinafter referred to as polyarylene ethers or PAE) as FAP. Their relative permittivities are from about 2.5 to 2.9, and their application to insulating films for electronic devices or multilayered wiring boards (hereinafter referred to as the present insulating films) is also being studied.
The arylene structure in such PAE may, for example, be perfluorophenylene, perfluorobiphenylene or perfluoronaphthanylene. And, PAE is linear, and its glass transition temperature (hereinafter referred to as Tg) is low, and thus, the heat resistance is not sufficient. If a crosslinkable functional group is introduced into PAE for crosslinking, Tg can be made high, but the relative permittivity will increase to a level of from 2.7 to 3.0, whereby it is difficult to satisfy both a low relative permittivity and high Tg simultaneously.
Bull. Chem. Soc. Jpn., 66, 1053 (1993), etc. disclose a fluorinated poly(1,4-phenylene) as linear FAP, but no application to the present insulating film is disclosed. Further, if the polymerization degree exceeds 3, the solubility in a solvent substantially decreases, and a coating property required by the present insulating film will be lost, and further, it will be sublimated by heat treatment during the process for producing an insulating film, whereby it can not be applied to the present insulating film.
J. Am. Chem. Soc., 122, 1832 (2000) discloses dendrimers as FAP having branched structures. These dendrimers can be dissolved in a solvent, but Tg is as low as lower than 140° C., and they have sublimability, whereby they can not be applied to the present insulating films.
The purpose of the present invention is to provide FAP having a low relative permittivity and high heat resistance, and its use as an insulating film.